A Cascade C(sp3)−H Annulation Involving C(alkyl),C(alkyl)‐Palladacycle Intermediates

Abstract C−H bond functionalization involving C , C ‐palladacycle intermediates provides a unique platform for developing novel reactions. However, the vast majority of studies have been limited to the transformations of C (aryl), C ‐palladacycles. In sharp contrast, catalytic reactions involving C (alkyl), C (alkyl)‐palladacycles have rarely been reported. Herein, we disclose an unprecedented cascade C(sp 3 )−H annulation involving C (alkyl), C (alkyl)‐palladacycles. In this protocol, alkene‐tethered cycloalkenyl bromides undergo intramolecular Heck/C(sp 3 )−H activation to generate C (alkyl), C (alkyl)‐palladacycles, which can be captured by α ‐bromoacrylic acids to afford tricyclic fused pyridinediones. In addition, this strategy can also be applied to indole‐tethered cycloalkenyl bromides to construct pentacyclic fused pyridinediones via suquential Heck dearomatization/C(sp 3 )−H activation/decarboxylative cyclization. Notably, the removal of α ‐bromoacrylic acids in the reaction of alkene‐tethered cycloalkenyl bromides can build an interesting tricyclic skeleton containing a four‐membered ring. Preliminary mechanistic experiments indicate that five‐membered C (alkyl), C (alkyl)‐palladacycles serve as the key intermediates. Meanwhile, density functional theory (DFT) calculations have provided insights into the reaction pathway.